Messages in this thread |  | | | Date | Sat, 28 Aug 2010 18:18:58 +0200 | | From | Sascha Hauer <> | | Subject | Re: [PATCH 3/3 v2] dmaengine: Add Freescale i.MX SDMA support |
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On Sat, Aug 28, 2010 at 05:27:10PM +0200, Marek Vasut wrote: > Dne So 28. srpna 2010 17:18:17 Linus Walleij napsal(a): > > 2010/8/23 Uwe Kleine-König <u.kleine-koenig@pengutronix.de>: > > >> + evt = readl(SDMA_H_EVTOVR); > > >> + mcu = readl(SDMA_H_HOSTOVR); > > >> + dsp = readl(SDMA_H_DSPOVR); > > > > > > __raw_readl? > > > > Sorry I never understood this __raw_[read|write][b|w|l] vs. > > plain read[b|w|l] proliferation in some drivers and code. > > > > What's the reason for? > > Hey, > > this trick is, if you create the VA<->PA mapping at the kernel start (eg. see > how pxa_map_io() is replacedon some devices for instance), you then use the VA > address you specified and use __raw_{read,write}[b,w,l](). So use > __raw_{read,write}[b,w,l]() on drivers specific for certain device and use > {read,write}[b,w,l]() on ioremap()ed memory areas, aka. in common drivers.
Nope, this has nothing to do with static mappings vs. ioremap. The difference is that read[b,w,l] do little endian accesses suitable for PCI whereas the __raw_* functions do accesses in CPU endianess. Peripherals integrated into a SoC like the SDMA engine here are normally accessible in native endianess and thus need the __raw_* functions. An external network controller (for example a LAN9117) will probably need the non raw functions. Note that 99% of the arm users use little endian only and thus cpu_to_le* is a noop, so both types will work for most people. Sascha
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